The present invention relates to a vibration damping apparatus which reduces vibrations of a structure such as an exposure apparatus used to fabricate various devices such as a semiconductor chip including an IC or LSI, a display element including a liquid crystal panel, a detection element including a magnetic head, and an image sensing element including a CCD, a control method for the vibration damping apparatus, an exposure apparatus having the vibration damping apparatus, a maintenance method therefor, a semiconductor device fabrication method, and a semiconductor fabrication factory.
Precision apparatuses such as an electron microscope and an exposure apparatus applied to a semiconductor fabrication process must minimize and cut off vibrations transferred from the outside and vibrations transferred to the outside, and must incorporate (or be mounted on) a vibration damping apparatus which reduces and cuts off vibrations. Particularly, in the exposure apparatus, an exposure X-Y stage continuously moves at a high speed. The vibration damping apparatus must realize high-precision vibration damping performance against external vibrations and high-precision vibration suppression performance against internal vibrations generated by the mounted apparatus itself.
To meet this demand, active vibration damping apparatuses have recently been put into practical use. This vibration damping apparatus can achieve effective vibration control by driving an actuator in accordance with a detection signal from a vibration sensor.
A passive vibration damping apparatus is comprised of only a support mechanism having spring and damper characteristics, and exhibits a tradeoff between the vibration damping performance and the vibration suppression performance. If the vibration damping performance is preferred in the passive vibration damping apparatus, low stiffness and low viscosity are demanded of the support mechanism. This demand degrades the vibration suppression performance.
The advantage of the active vibration damping apparatus is that it can satisfy both the vibration damping performance and vibration suppression performance. The vibration sensor and actuator can realize the viscosity and stiffness of a skyhook whose fulcrum is an absolute rest point in the space.
The feature of the active vibration damping apparatus is to set a vibration sensor on a vibration damping table which supports a precision apparatus and to feed back a detection signal from the vibration sensor to the actuator. A vibration damping apparatus disclosed in Japanese Patent Laid-Open No. 2000-274482 (active vibration damping apparatus, exposure apparatus and method, and device fabrication method) adopts a feedback loop which applies the stiffness of a skyhook to a vibration damping table together with the viscosity of the skyhook. According to this reference, the vibration damping apparatus has a vibration measurement unit which measures vibrations of the vibration damping table and those of an actuator serving as an air spring which supports the vibration damping table. By supporting the vibration damping table by a stiffness element such as the actuator serving as an air spring, vibrations transferred from the installation floor to the vibration damping table are cut off. The vibration damping apparatus also comprises an acceleration/velocity feedback loop. An acceleration and velocity based on an output from the vibration measurement unit are fed back to the actuator serving as an air spring, applying the viscosity and stiffness of the skyhook to the vibration damping table. The xe2x80x9cskyhookxe2x80x9d means that an absolute rest point in the space is used as a fulcrum. The viscosity and stiffness of the skyhook keep the vibration damping table absolutely at rest. The stiffness suppresses displacement, and the viscosity quickly damps residual vibrations.
For effective vibration control, a vibration damping apparatus having both the viscosity and stiffness of a skyhook is desirable, as disclosed in the reference. Most of conventional vibration damping apparatuses realize only the skyhook viscosity through a feedback loop. The first step of vibration control is to damp residual vibrations, and many vibration damping apparatuses are equipped with only a minimum function of realizing the skyhook viscosity.
However, only the viscosity cannot fully demonstrate the ability of the vibration damping apparatus. Realization of the skyhook stiffness is desired for higher-precision vibration control.
One of the reasons why no conventional vibration damping apparatus realizes the skyhook stiffness is that an acceleration sensor has conventionally been used for vibration measurement in the vibration control field, as considered in Japanese Patent Laid-Open No. 2000-274482 described above. The acceleration sensor, also called a tilt sensor, can detect from a direct current to a high-frequency component. When, however, vibrations are actually measured using the acceleration sensor, almost no very low frequencies are observed. The physical quantity of velocity is a first-order integral of the acceleration, and the velocity sensor has a higher sensitivity to a lower frequency than the acceleration sensor. In other words, the velocity sensor is more advantageous than the acceleration sensor to low-frequency vibration measurement. The skyhook stiffness contains a low-frequency component in the control band, and the above reference realizes effective skyhook stiffness by using the velocity sensor.
There is another technical problem which obstructs realization of the skyhook stiffness. This problem is changes in a natural mode accompanying application of the stiffness. The rigid-body motion of the vibration damping table has natural modes equal in number to the degree of freedom of motion. From the viewpoint of dynamics, the vibration damping table is modeled into a stiffness element, and the air spring which supports the vibration damping table is modeled into a stiffness element (spring element). As is well known, the rigid-body spring system has natural modes equal in number to the degree of freedom of motion of the rigid body. Thus, the rigid-body motion of the vibration damping table has a natural mode which is a phenomenon unique to the rigid-body spring system.
The frequency in the natural mode is called a natural frequency, and the direction or state of the natural mode is called a mode shape. Upon applying disturbance vibrations similar in direction to frequency, vibrations excited in the system are converted into a natural mode. That is, not only are various vibrations generated in the vibration damping table, but also, vibrations are excited mainly in the natural mode.
The skyhook viscosity so acts as to apply damping to the natural mode. It should be noted that the natural mode is kept unchanged regardless of the presence/absence of viscosity. This is because the natural mode is determined by the inertia and stiffness of the system regardless of the viscosity. As long as the feedback loop which realizes the viscosity is appropriate, damping can be applied to all natural modes.
The skyhook stiffness influences the natural mode. The skyhook stiffness applies new stiffness using the space as a fulcrum to the vibration damping table, and the natural mode changes depending on the presence/absence of the stiffness. Changes in natural mode should be prevented because of the following reasons.
First, the natural mode is a basic design specification in the design of a mechanical structure such as a vibration damping apparatus. The movable direction and range of a movable mechanism are designed based on the natural mode. This also applies to the layout of the vibration sensor and actuator, and their layout is determined in consideration of the observability and controllability of the natural mode. The mechanical structure of the vibration damping apparatus is designed based on the natural mode, and the natural mode is desirably kept unchanged regardless of the presence/absence of the feedback loop.
Second, changes in natural mode inhibit the performance evaluation of the vibration damping apparatus. The primary role of the vibration damping apparatus is to cut off vibrations transferred from the installation floor. The floor vibration transmissibility is one of indices for performance evaluation. The floor vibration transmissibility is measured by installing vibration sensors on both the vibration damping table and installation floor in two horizontal directions and the vertical direction. Measurement in the two horizontal directions and the vertical direction is performed because the sense of directions is clear and the vibration sensors basically detect vibrations in horizontal or vertical translation. In general, the vibration damping table has natural modes corresponding to translations in the two horizontal directions and the vertical direction. With the presence of such natural modes, vibrations from the installation floor and vibrations from the vibration damping table exhibit a high correlation upon measurement by the vibration sensors. Thus, the floor vibration transmissibility can be measured at a high precision. Application of the skyhook stiffness may decrease the measurement precision of the floor vibration transmissibility. This is because applying the stiffness may change the natural mode in a direction different from translations in the two horizontal directions and the vertical direction. Considering the performance evaluation of the vibration damping apparatus, the natural mode is desirably kept unchanged.
Third, the natural mode is a basic design specification of the vibration damping apparatus, but an improper natural mode different from the design may be realized. The natural mode becomes different from the design owing to characteristic variations of the structure of the vibration damping apparatus and the shape and weight of a precision apparatus mounted on the vibration damping table. This inhibits smooth operation of the movable mechanism of the vibration damping apparatus and the layout of the vibration sensor and actuator. In this case, the natural mode is desirably shaped into a proper one by a feedback loop operation.
The present invention has been made in consideration of the above situation, and has as its object to provide a vibration damping apparatus capable of fixing the natural mode of the rigid-body motion of a vibration damping table even upon applying the stiffness of a skyhook to the vibration damping table in a feedback lop.
It is another object of the present invention to provide a vibration damping apparatus capable of arbitrarily adjusting the natural mode of the rigid-body motion of the vibration damping table.
To solve the conventional problems and to achieve the above objects, there are provided a vibration damping apparatus and a control method, comprising a vibration damping unit which reduces vibrations of a structure, a support unit which supports the vibration damping unit, an actuator which applies a vibration suppression force to the vibration damping unit, a vibration sensor which detects vibrations of the vibration damping unit, and a controller having a feedback loop which so controls as to drive the support unit and the actuator in accordance with a detection result of the vibration sensor and to apply stiffness, viscosity, and inertia to the vibration damping unit, wherein the controller applies the inertia in accordance with physical parameters of the vibration damping unit and the support unit and the stiffness so as not to change a natural mode of rigid-body motion of the vibration damping unit depending on the presence/absence of the feedback loop.
Also, there are provided a vibration damping apparatus and a control method therefor according to the present invention, comprising a vibration damping unit which reduces vibrations of a structure, a support unit which supports the vibration damping unit, an actuator which applies a vibration suppression force to the vibration damping unit, a vibration sensor which detects vibrations of the vibration damping unit, and a controller having a feedback loop which so controls as to drive the support unit and the actuator in accordance with a detection result of the vibration sensor and to apply stiffness, viscosity, and inertia to the vibration damping unit, wherein the controller applies the stiffness in accordance with physical parameters of the vibration damping unit and the support unit and the inertia so as not to change a natural mode of rigid-body motion of the vibration damping unit depending on presence/absence of the feedback loop.
According to these apparatuses and methods, the vibration damping unit which supports a precision apparatus or the like is supported by an air spring serving as the support unit. The actuator such as a linear motor applies a vibration suppression force to the vibration damping unit. The air spring functions as a support leg which supports the vibration damping unit, and as an actuator which controls the internal pressure to apply a vibration suppression force to the vibration damping unit. The vibration sensor detects vibrations of the vibration damping unit. xe2x80x9cVibrationsxe2x80x9d mean the absolute acceleration and velocity of the vibration damping unit with respect to the space. The stiffness and viscosity of the skyhook and the inertia are applied to the vibration damping unit by driving actuators such as the air spring and linear motor in accordance with an output from the vibration sensor. In general, application of the stiffness to the vibration damping unit changes the natural mode of the rigid-body motion of the vibration damping unit. The inertia is so applied as to keep the natural mode unchanged. The inertia is applied in accordance with the physical parameters of the vibration damping unit and air spring, and application of the stiffness. The physical parameters of the vibration damping unit and air spring mean the mass, moment of inertia, and inertia product of the vibration damping unit, the stiffness of the air spring SU, and the like.
Also, there are provided a vibration damping apparatus and a control method therefor according to the present invention, comprising a vibration damping unit which reduces vibrations of a structure, a support unit which supports the vibration damping unit, an actuator which applies a vibration suppression force to the vibration damping unit, a vibration sensor which detects vibrations of the vibration damping unit, and a controller having a feedback loop which so controls as to drive the support unit and the actuator in accordance with a detection result of the vibration sensor and to apply stiffness, viscosity, and inertia to the vibration damping unit, wherein the controller applies the inertia in accordance with physical parameters of the vibration damping unit and the support unit and the stiffness so as to arbitrarily adjust a natural mode of rigid-body motion of the vibration damping unit.
Also, there are provided a vibration damping apparatus and a control method therefor according to the present invention, comprising a vibration damping unit which reduces vibrations of a structure, a support unit which supports the vibration damping unit, an actuator which applies a vibration suppression force to the vibration damping unit, a vibration sensor which detects vibrations of the vibration damping unit, and a controller having a feedback loop which so controls as to drive the support unit and the actuator in accordance with a detection result of the vibration sensor and to apply stiffness, viscosity, and inertia to the vibration damping unit, wherein the controller applies the stiffness in accordance with physical parameters of the vibration damping unit and the support unit and the inertia so as to arbitrarily adjust a natural mode of rigid-body motion of the vibration damping unit.
According to these apparatuses and methods, the inertia is so applied as to arbitrarily adjust the natural mode of the rigid-body motion of the vibration damping unit. The inertia is applied in accordance with the physical parameters of air springs serving as the vibration damping unit and support unit, and application of the stiffness.
It is preferable that a correspondence table between the stiffness and the inertia be held in advance, and the feedback loop be operated in accordance with the correspondence table.
An exposure apparatus according to the present invention comprises the above vibration damping apparatus.
The present invention can be applied to a semiconductor device fabrication method comprising the step of installing fabrication apparatuses for performing various processes, including the exposure apparatus of the present invention, in a semiconductor fabrication factory, and the step of fabricating a semiconductor device by performing a plurality of processes using the fabrication apparatuses.
The semiconductor device fabrication method preferably further comprises the step of connecting the fabrication apparatuses by a local area network, and the step of communicating information about at least one of the fabrication apparatuses between the local area network and an external network outside the semiconductor fabrication factory.
Preferably, a database provided by a vendor or user of the exposure apparatus is accessed via the external network to obtain maintenance information about the fabrication apparatus by data communication, or data communication is performed between the semiconductor fabrication factory and another semiconductor fabrication factory via the external network to perform production management.
The present invention can be applied to a semiconductor fabrication factory comprising fabrication apparatuses for performing various processes, including the exposure apparatus of the present invention, a local area network which connects the fabrication apparatuses, and a gateway which allows the local area network to access an external network outside the factory, wherein information about at least one of the fabrication apparatuses can be communicated.
The present invention can be applied to a maintenance method for the exposure apparatus of the present invention that is installed in a semiconductor fabrication factory, comprising the step of causing a vendor or user of the exposure apparatus to provide a maintenance database connected to an external network outside the semiconductor fabrication factory, the step of granting access to the maintenance database in the semiconductor fabrication factory via the external network, and the step of transmitting maintenance information accumulated in the maintenance database to the semiconductor fabrication factory via the external network.
The exposure apparatus according to the present invention further comprises a display, a network interface, and a computer which executes network software, and maintenance information about the exposure apparatus can be communicated via a computer network.
The network software preferably provides on the display a user interface for accessing a maintenance database which is provided by a vendor or user of the exposure apparatus and connected to an external network outside a factory where the exposure apparatus is installed, and enables obtaining information from the database via the external network.
As described above, according to the present invention, vibrations of the vibration damping table are suppressed by applying the stiffness and viscosity of the skyhook and the inertia to the vibration damping table. The natural mode of the rigid-body motion of the vibration damping table is kept unchanged regardless of the presence/absence of the feedback loop. Hence, a feedback loop for each motion mode operates preferably. The movable range of the vibration damping apparatus and the layout of the vibration sensor and actuator need not be redesigned. According to the present invention, the natural mode of the rigid-body motion of the vibration damping table can be arbitrarily adjusted. The natural mode can be shaped into a desirable one. The present invention can provide a vibration damping apparatus capable of preferable vibration damping control, and a high-precision semiconductor exposure apparatus having the vibration damping apparatus.
Other objects and advantages besides those discussed above shall be apparent to those skilled in the art from the description of a preferred embodiment of the invention which follows. In the description, reference is made to the accompanying drawings, which form a part thereof, and which illustrate an example of the invention. Such an example, however, is not exhaustive of the various embodiments of the invention, and, therefore, reference is made to the claims which follow the description for determining the scope of the invention.